Investigating the relationship between the superconducting and pseudogap states of the high-temperature superconductor Bi-2201 using scanning tunneling microscopy

There is considerable controversy regarding the nature of the relationship between the superconducting and pseudogap states of high-temperature superconductors. Although there exist a large number of theories regarding their relationship, the theories fall into one of two broad classes. The first class views the superconducting state as intrinsically tied to the pseudogap state. The second class views the pseudogap state as unrelated to or possibly competing with superconductivity. To address this controversy, we utilize a custom, home-built scanning tunneling microscope (STM) with the ability to follow the same atomically resolved location as a function of temperature to study the high-temperature superconductor Bi2Sr2CuO6s+. In our studies we are able to track the spatial evolution of the local density of states as the temperature is raised through the superconducting transition temperature, Tc, and in doing so, understand how the density of states evolves from the superconducting to pseudogap states. This thesis contains three complementary studies, all of which give some insight into the two states. The main study of this thesis focuses on the spatial evolution of the gap in the density of states, from below to above Tc in overdoped Bi2Sr2CuO6+8 (Tc = 15 K). Initially we find a spatially inhomogeneous gap which smoothly evolves with temperature through Tc. However, from the temperature and spatial dependence of the spectra, we are able to employ a normalization scheme which leads us to uncover a small, spatially homogeneous gap which coexists with the larger gap throughout the sample and disappears at Tc. From a study of the doping dependence of the two gaps, we determine that the large gap is the pseudogap, that the small gap is the superconducting gap, and that they appear to be two independent gaps indicating that they are associated with two apparently separate phases.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2008

Author dc:creator

• Boyer, Michael Christopher

Advisor dc:contributor.advisor

• Eric W. Hudson.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/45453

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45453